a, 9x+5-(x+20)=4(x+20)+2 b,5(x-6)=20(x-5)+2(x+30)

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1. Câu `a` :

   `9x+5 – (x+20) = 4(x+20)+2`

   `=> 9x +5 – x – 20 = 4x + 80 +2`

   `=> 8x – 15 = 4x + 82`

   `=> 8x – 4x = 82 +15`

   `=> 4x = 97`

   `=> x = 97/4`

   Câu `b` :

   `5(x-6) = 20(x-5) + 2(x+30)`

   `=> 5x – 30 = 20x – 100 + 2x + 60`

   `=> 5x – 30 = 22x – 40`

   `=> -30 +40= 22x-5x`

   `=> 10 = 17x`

   `=> x = 10/17`

    

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2. Đáp án:

   `a,`

   `9x + 5 – (x + 20) = 4 (x + 20) + 2`

   `⇔ 9x + 5 – x – 20 = 4x + 80 + 2`

   `⇔ (9x – x) + (5 – 20) = 4x + (80 + 2)`

   `⇔ 8x – 15 = 4x + 82`

   `⇔ 8x – 4x = 15 + 82`

   `⇔ (8 – 4)x = 97`

   `⇔ 4x = 97`

   `⇔ x = 97 ÷ 4`

   `⇔ x  =97/4`

   `text{Vậy}` `x = 97/4`

   `b,`

   `5 (x – 6) = 20 (x – 5) + 2 (x + 30)`

   `⇔ 5x – 30 = 20x – 100 + 2x + 60`

   `⇔ 5x – 30 = (20x + 2x) + (-100 + 60)`

   `⇔ 5x-30=22x – 40`

   `⇔ 5x – 22x = 30 – 40`

   `⇔ (5 – 22)x = -10`

   `⇔ -17x = -10`

   `⇔ x = -10 ÷ (-17)`

   `⇔ x = 10/17`

   `text{Vậy}` `x = 10/17`

    

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